Sonic vibration baffles

ABSTRACT

The tubular elements which make-up the tube bundles in the gas duct of a furnace are arranged in a manner which prevents formation of destructive standing waves by the gas stream in the duct. The tubular elements are generally in side by side relationship across the gas duct and each comprise a number of tube runs which are spaced in the direction of gas flow and are transverse thereto. The majority of the tubular elements occupy one positioning in the direction of gas flow and a selected minority of tubular elements are offset in the direction of gas flow such that their tube runs impede or baffle the lateral motion of the gas stream which gives rise to standing waves. Those tubular elements which are offset are at or near locations across the duct at which baffle plates have formerly been used to prevent formation of standing waves.

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Chayes [451 Mar. 2, W72

[54] SUNHC VIBRATION BAFFLES [72] Inventor: Norman C. Chayes, Bloomfield, Conn.

211 Appl. No.: 91,503

Primary Examiner-Kenneth W. Sprague Attorney-Carlton F. Bryant, Eldon H. Luther, Robert L. Olson, John F. Carney, Richard H. Berneike, Edward L. Kochey, Jr. and Lawrence P. Kessler [57] ABSTRACT The tubular elements which make-up the tube bundles in the gas duct of a furnace are arranged in a manner which prevents formation of destructive standing waves by the gas stream in the duct. The tubular elements are generally in side by side relationship across the gas duct and each comprise a number of tube runs which are spaced in the direction of gas flow and are transverse thereto. The majority of the tubular elements occupy one positioning in the direction of gas flow and a selected minority of tubular elements are offset in the direction of gas flow such that their tube runs impede or baffle the lateral motion of the gas stream which gives rise to standing waves. Those tubular elements which are offset are at or near locations across the duct at which baffle plates have formerly been used to prevent formation of standing waves.

6 Claims, 6 Drawing Figures ["A'IENTFHWPH1W2 3,651,788

5mm 1 UP 3 INVENTOR.

NORMAN C. CHAYES FIG. I ATTORNEY PATENTEUMAR28 I972 GAS FLOW GAS FLOW sum 2 BF 3 I III I Ill/I Ill FIG.3 1

\ W b V Ci 0 v DWZZO W INVFNT 0 c 0 Q w C1532 U U BY. 7 FIG. 6 [A QLO ATTORNEY PATENTEH 2 5M253 IEWE ma 3 BF 3 GAS FLOW ATTORNEY SONIC VIBRATION BAFFLES BACKGROUND OF THE INVENTION The invention relates to the problem of acoustical standing wave vibrations produced as a result of a gas passing through a duct and over tubular bundles extending transversely of the gas stream and more particularly to an arrangement of the tubes in said tube bundles in a manner which serves to baffle the duct and prevent formation of standing waves therein.

In arrangements wherein a gas flowing through a gas duct is caused to pass over a plurality of tubular elements disposed generally transversely of the gas flow, certain combinations of conditions may give rise to the formation of acoustical standing waves in the gas column passing through the duct. Such standing waves may exist in the horizontal and vertical gas pass sections of a steam generator furnace where many tubular elements are located in bundles to serve a heat exchange function. Each of these tubular elements is normally a sinuously bent tube with its tube runs disposed transversely of the direction of gas flow and successive tube runs in a particular element are spaced in the direction of gas flow. A plurality of these tubular elements exist in parallel side by side relation extending across the width of the gas pass. This arrangement of tubular elements disposed transversely of the gas flow stream gives rise to the phenomenon referred to as the von Karman Trail" in which swirling gas vortices form immediately downstream of the tubular elements and oscillate laterally of the gas flow stream. This oscillation of the vortices is referred to as vortex shedding. The frequency of this vortex shedding is determined largely by the temperature and velocity of the gas stream. When a condition exists wherein a plurality of tubular elements in the gas stream create considerable vortex shedding energy at some frequency and further the gas cavity geometry is in resonance with the vortex shedding frequency, an acoustical standing wave of significant amplitude may be developed. A more detailed description of this phenomenon may be found in U.S. Pat. No. 2,893,509 and additionally in U.S. Pat. No. 3,263,654.

The standing waves created by this phenomenon can be destructive to the tube elements in the gas stream and the duct work and further, may be extremely annoying to plant personnel because of the intensity of their audibility. Therefore, various means have been employed to contend with this problem. In U.S. Pat. No. 2,893,509 a tube arrangement is provided wherein a plurality of vortex shedding frequencies exist at any one time in the tube bundles and insufficient energy exists at any one frequency for a condition of resonance to exist. Such an arrangement, though effective, is difficult and expensive to fabricate. The means most commonly employed consists of baffle plates discretely positioned in the gas duct and extending along the gas flow stream. These baffles serve to detune or deresonate the cavity formed by the gas duct by blocking the lateral displacement of the gas caused by vortex shedding. The number and placement of these baffles is chosen to deresonate the duct for the various standing wave forms which otherwise could form, thereby preventing their formation. U.S. Pat. No. 3,263,654 discusses the basic half wave standing wave and the harmonics thereof which may exist under various conditions of gas velocity, gas temperature, and tube and duct geometry. It further describes a relationship for determining the placement of baffles within the gas pass duct. The placement of the baffles along the gas stream and between the walls of the gas duct serves to detune the duct cavity for the various possible standing waves which might exist.

The baffles conventionally used to detune the gas pass duct are sheets of stainless steel which extend across the depth of the gas pass duct and in many instances extend much of the length of the gas pass duct. These baffles, while effective, are costly to purchase and install and have a restricted useful life because of the high temperatures encountered in the environment in which they are used. To date the greatest problem with standing waves has existed in the vertical gas pass of a furnace, however, increasing gas temperatures and velocities may result in a similar problem in some portions of the pendant tube bundles of the horizontal gas pass portion of the furnace. In this latter mentioned area of the furnace, the life of a metal sheet baffle will be even less because of increased temperatures in this area.

SUMMARY OF THE INVENTION According to the invention, selected fluid cooled tube elements within a tube bundle are positioned relative to the remaining tubes in the bundle such that a baffling effect is created and formation of the destructive standing waves is prevented. This positioning of the selected tube elements is such that lanes which extend transversely of the gas flow and the tube runs are blocked.

Lanes are formed between successive tube runs of a tube element and when adjacent tube elements have the same spacing between tube runs and exist in side by side relation across the gas duct, the lane will extend across the gas duct. Lateral displacement of the gas stream in these lanes because of vortex shedding is essential for the formation of standing waves and impediments to this lateral displacement serve to prevent the formation of the standing waves.

A baffle is most effective in eliminating standing wave formation if located at a displacement maximum of the potential standing wave. Because not only first harmonic standing waves but also successive integral harmonic waves may exist in the gas duct, baffles may be required at a plurality of locations across the width of the gas duct. Preferred locations for the placement of the anti-vibration baffles have generally been determined as a function of the width of the gas pass duct in a manner similar to that described in U.S. Pat. No. 3,263,654.

According to my invention, tube elements at or near such above mentioned preferred baffling locations are located or relocated along the direction of gas flow such that their tube runs occupy and block the lanes which extend laterally of the main gas flow. In tube bundles wherein the center line spacing between successive tube runs of a tube element is about twice the tube diameter, a single tube element at each preferred baffling location positioned along the gas stream such that its tube runs are intermediate the successive tube runs of the other tube elements will be effective to provide the desired baffling effect and thereby prevent formation of the standing waves. In tube bundles wherein the center line spacing between successive tube runs of a tube element is several times the tube diameter, a plurality of tube elements at each preferred baffling location may be differently positioned along the gas stream relative to one another and the remaining majority of tube elements in order to effect blockage of the lanes created by the majority of tube elements and thereby serve as a baffle.

In many furnaces and particularly in the vertical gas pass of the furnace, the tube bundles are supported by support tubes which depend or hang from the top of the furnace. These tubes, like those of the tube bundles, are cooled by a working fluid passing therethrough. Usually the tube elements are supported in adjacent pairs by support tubes passing therebetween. In accordance with the invention the support tubes at the preselected baffling locations are extended or shortened by an amount which positions a pair of commonly supported tube elements such that their tube runs occupy and block the lateral lanes created by the remaining tube runs and thereby prevents formation of standing waves.

The tube arrangement of the invention while finding most immediate application in the vertical gas pass of a furnace and described with reference thereto also finds application in the horizontal gas pass of a furnace. In the horizontal gas pass of a furnace, the tube arrangement relative to gas flow is the same and the desired baffling effect is obtained in that instance by off-setting the position of the selected tube elements horizontally in the direction of gas flow to the extent required. Use of the tube elements to provide the required baffling is particularly appealing in the horizontal gas pass of the furnace because of gas temperatures there even higher than in the rear pass. As in the vertical gas pass, the required baffling is accomplished by some of the normally present fluid cooled tube elements.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic representation of a vertical section of a modern steam generator.

FIG. 2 is an illustration of the vortices formed in a gas stream upon passage of the gas stream over a tubular element oriented transversely thereto.

F IG. 3 is a diagrammatic representation of a sectional view of the rear vertical gas pass taken along line 3-3 of FIG. 1.

FIG. 4 is an enlarged sectional view of a portion of the rear vertical gas pass taken along line 44 of FIG. 1 showing a basic form of the tube arrangement of the invention.

FIG. 5 is an enlarged view of the upper left portion of FIG. 4 showing the tube arrangement of the invention in greater detail.

FIG. 6 is an enlarged sectional view of a portion of the vertical gas pass taken along line 66 of FIG. 3 showing a preferred constructional organization between the horizontal tube elements and the vertical support tubes which incorporates the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing and particularly to FIG. 1 thereof, the steam generator illustratively disclosed therein comprises a furnace 10 which is lined with vertically disposed steam generating tubes 12 and which is fired by means of the burners 14. The combustion gases evolved by the burning of fuel within the furnace pass upwardly through the furnace and out through the horizontal gas pass or duct 16 which is connected to the upper end of the vertically disposed gas pass or duct 18 with the combustion gases, after passing horizontally through duct 16, being conveyed downwardly through this duct 18 and out the bottom thereof to a suitable stack or other heat exchange apparatus. The steam that is generated in tubes 12 is collected in steam and water drum 20 where it is separated from the circulating water by means of suitable apparatus with the steam then being conveyed to the superheater of the steam generator where it is superheated as required for delivery to the turbine or the like.

In the illustrative organization the superheater is made up of low temperature section 22 which is positioned within vertical gas pass 18 and high temperature section 24 positioned at the outlet of furnace l0 and within the horizontal gas pass 16. These low and high temperature superheater sections are each made up of a large number of tubes or tube elements which are sinuously bent with the tubes being disposed in vertical planes spaced across the gas pass so as to form tube bundles with the tubular elements thereof in closely spaced relation. As is indicated in FIG. 1 it is the general practice to provide one or more wide vertical spaces or cavities within the low temperature superheater tube bundles 22 so as to form what is in effect spaced tube bundles 22a with there being three such bundles in the illustrative superheater section 22.

The saturated steam from drum 20 is conveyed via conduits 26 to the intermediate header 28 from which it passes to distribution headers 30 through conduits 32. From these headers 30 the the steam passes through the tubes of low temperature superheater section 22 after which it is conveyed through conduit 34 to the high temperature section 24. The partially superheated steam is finally superheated to its desired temperature upon passing through this high temperature superheat section with this steam being collected in header 36 from which it is conveyed to the turbine through conduit 40. After a portion of the energy of the steam has been utilized it is returned to the generator for reheating in the reheater 42 which is constructed of sinuously bent tubes in the same manner as the superheater and is positioned in duct 16 immediately to the rear of high temperature superheater section 24. Positioned downstream of low temperature superheater section 22 is the economizer 44 by means of which the feed water for the steam generator is heated and which is likewise fabricated of sinuously bent tubes in the same manner as the superheater. The feed water enters the economizer 44 through support tubes 46 which are affixed to the top of vertical gas pass 18 and depend vertically therefrom. The tubes of bundles 22a are afi'ixed, as by welding, to the support tubes 46 and receive most or all of their positional support therefrom.

It has been the practice to make these various heat exchange portions of the generator, which are comprised of sinuously bent tubes, by arranging the tubes or the tube runs which extend across the gas pass in parallel relation with each other and transversely of the duct or passageway within which the tubes are disposed. Thus the tube runs in the economizer and the low temperature superheater were horizontal while the tube runs in the reheater and high temperature superheater were vertical. With this particular design severe pulsation-induced vibration and noise has occurred in the ducts within which these tube bundles are disposed to the point of endangering the physical structure of the boiler.

FIG. 2 shows the vortices 48 which are formed by the gas flowing over the transversely disposed tubes of the several tube bundles. These vortices move or pulsate laterally from one side to the other at a frequency known as the vortex shedding frequency. In a duct in which a plurality of tubular elements transverse to the gas flow each have attendant vortex shedding. a standing wave will be created if the vortex shedding frequency is in resonance with the cavity defined principally by the side walls of the duct. The condition of resonance is determined and affected by factors such as gas velocity and temperature, duct width, and the lateral and transverse spacing of the tubular elements. Further, the standing wave established may be a simple half wave of the first harmonic or it may be an integral harmonic thereof depending on the factors previously mentioned.

Previously most common method of eliminating the standing wave has been with baffle plates in the ducts and which are parallel to both the normal gas flow and the tube runs and which are so spaced across the duct width that they break up the regular pattern of any wave which might try to form. The spacings of these baffle plates for the optimum detuning of a duct may be determined after vibrations have been detected or, in a less exact manner, may be approximated from various correlations prior to operation. One such correlation is disclosed in US. Pat. No. 3,263,654, however, increased gas temperatures and velocities during plant operation have narrowed the duct width required for half wave formation and bafi'ling may be required for duct widths as narrow as 12 to 15 feet.

The scope of the present invention is not intended to state or rely upon any specific or single relationship or correlation for determining baffling locations, but rather relates to the apparatus and technique for effecting said baffling once the preferred baffling locations have been determined by calculation or experience. In the exemplary arrangement described hereinafter, the tube organization of the invention will be described as located in the vertical gas pass 18 and for geometries and operating conditions which would normally suggest placing baffles at positions 8,, B and B ofgas pass 18 as shown in FIG. 3. In this instance the duct width is about 33 feet and the preferred spacings between one side wall of gas pass 18 and successive baffles are respectively 9, 20, and 28 feet. These spacings, while typical, are only intended to be exemplary. The locations selected for baffling should not occur at the displacement nodes of the several standing wave forms which they seek to prevent, or more importantly, they should exist at locations which are at or near the gas displacement maximums which would exist for each of the several harmonics of wave forms which might occur. This then suggests the non-uniform spacing of FIG. 3.

As taught by the prior art, baffle plates would extend from the front to the rear of vertical gas pass duct 18 at the posi- IOI029 0121 tions or locations designated as B,, B and B and would extend with the gas flow through several of the tube bundles in the duct and in some instances into the cavities between tube bundles. According to the invention, however, the baffle plates are omitted and instead tube elements at or near locations B B B etc., are so positioned relative to the remaining majority of tubes in a particular tube bundle that they have a baffling or blocking effect on the laterally oscillating gas in the lanes existing between successive tube runs of the bundle.

FIG. 4 depicts the several spaced tube bundles 22a of the low temperature superheater 22 and the tube arrangement of the invention. All of the tube runs of a tube element extend transversely of or normal to the gas stream in gas pass 18 and each successive tube run of a tube element is spaced from the previous in the direction of gas flow, in this instance vertically. For ease of description the arrangement of the tube runs of a tube element in the direction of gas flow is termed a file. Accordingly, file F is comprised of the vertically spaced and aligned tube runs of the tube element closest to a side wall of gas pass 18. Each tube bundle is comprised of a plurality of tube elements and associated tube runs in spaced side by side relationship across the width of gas pass 18, thus forming tube run files F F F E The lateral or side by side arrangement of the tube runs of the several tube elements at a certain position along the gas stream, here a certain vertical location, is termed a rank. The spacing between the consecutive tube runs of a tube element is the same for each tube element and the majority of tube elements are arranged in parallel spaced side by side relationship across gas pass 18 at the same elevation, thus forming major ranks R R R etc., of the tube runs.

FIG. 5 is an enlarged view of a portion of FIG. 4 showing several files of tube runs and several major ranks of tube runs. Between adjacent tube runs in a file there is a space and the tube runs of adjacent major ranks define a space extending horizontally or laterally across normally the entire duct, forming a lane. The lanes between each major rank of tube runs are designated L L L etc., and they allow the lateral gas oscillation which forms the standing waves. However, in accordance with the invention certain of the files of tube runs, such as F are so positioned in the direction of gas flow with respect to the other files that the tube runs interrupt or block the lateral continuity of the lanes. This has the efi'ect of greatly impeding lateral movement of the gas stream at these locations and if the locations are selected to coincide with those normally used for battle plates, formation of the acoustical standing waves is prevented.

The certain files of tube runs selected to block lateral gas flow are positioned along the gas stream such that their tube runs are intermediate the major ranks of tube runs and are normally in lateral alignment with one another, and accordingly, form minor ranks R R R etc.

In FIG. 4 the tubes of files F F and F have been positioned such that their respective tube runs are in lateral alignment to form minor ranks R R R etc., which occupy respectively, lanes L L L etc. The tubes which form these minor ranks and serve to baffle the gas pass 18 are selected to coincide with the positions B B and B of FIG. 3 at which baffle plates would formerly have been located. These tubes are hereinafter referred to as the baffle tubes.

In the superheater bundles 22a of gas pass 18 the tubes conventionally are of 2% inch diameter and the center line spacing between tube runs in a file is about 5 inches. Positioning the center lines of the tube runs of the minor ranks midway between the center lines of tube runs of the major ranks in the direction of gas flow blocks lateral gas flow sufficiently to prevent formation of standing waves. This arrangement is also effective where the spacing between tube run center lines is somewhat greater than twice the tube diameter.

Positioning of the tube elements within vertical gas pass 18 is generally accomplished by support tubes 46. Support tubes 46 are affixed to and depend from the structure at the top of vertical gas pass lb and are cooled by the working fluid which they conduct. Typically, support tubes are located adjacent each end of the tube runs and laterally adjacent pairs of tube elements are affixed to and supported by these support tubes.

FIG. 6 depicts a preferred tube arrangement according to the invention wherein the center line spacing between the tube runs of a tube element is about twice the diameter of a tube. The tube runs of the tube elements which form files F and F are affixed to support tube 46 it being the closest to a preferred baffling location 8,. The offset positioning of the baffle tubes relative to those forming the major ranks is accomplished either by vertically shifting the points at which the tube runs of the baffle tube are affixed to support tube 4,6 or with the tube runs affixed adjusting support tube 46 upwardly or downwardly with respect to tube bundles 22a. Either method of effecting positioning of the baffle tubes is easily accomplished during original construction and the latter method of vertically adjusting the support tubes is a particularly easy field modification. The field modification may be made by cutting the relevant support tubes and associated baffle tube elements beyond the vertical extremities of the tube bundles, adding and subtracting the necessary vertical length to the severed tube stubs and rejoining the support tubes and associated baffle tube elements at that vertical positioning in which they effectively block lateral gas flow in the lanes as taught by the invention.

In the event that the center line spacing between the consecutive tube runs of a tube element is several times the diameter of the tubes in the tube bundle, it may be desirable to use a plurality of baffle tubes or adjacent pairs of baffle tubes at each of the baffling locations to block the lanes L,,,,, L L

etc. In that instance, each one or adjacent pair of the baffle tubes at a particular baffling location is differently positioned along the gas stream relative to the other baffle tube or tubes at that location to form a plurality of minor ranks of tube runs between each of the major ranks such that lateral gas flow at that location is substantially prevented.

The preceding arrangement of tube elements and support tubes was described for the horizontal tubular heat exchange elements in the vertical gas pass of a furnace. It will be readily appreciated that the same baffling effect, using only tubular heat exchange elements, can be obtained in the horizontal gas pass 16 where the tube elements are pendently supported at the top of the furnace and extend vertically downwardly therefrom. In that region of horizontal gas How the tubes at the preferred baffling locations across the width of the gas duct are relocated in the direction of gas flow to block the lateral gas oscillations which may occur in the lanes between the consecutive tube runs. This is a horizontal repositioning" of the selected baffling tubes rather than vertical as was the case in vertical gas pass 18. However, because the gas dynamics are the same the result obtained with the baffle tubes is also the same.

The tube arrangement of the invention replaces the baffle plates previously required in the tube bundle areas of the gas ducts to prevent standing wave formation. If baffling should be required in the duct cavities between the tube bundles, small baffle plates may be used in those areas.

While I have illustrated and described a preferred embodiment of my invention, it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. I, therefore, do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

What is claimed is:

l. In combination a tube bundle within a duct through which a gaseous stream is conveyed and wherein the tube runs of the tube elements of said bundle are disposed transversely of the direction of How of said stream, with there being numerous tube runs arranged in a plurality of aligned files, the tube runs in each file being parallelly spaced in the direction of gas flow, the tube runs of a substantial majority of said files so positioned and spaced in the direction of gas flow to form parallelly spaced major ranks of tube runs, each rank extending laterally across the gas stream and comprised of tube runs in spaced side by side relation, adjacent major ranks creating lanes therebetween extending laterally of the gas stream, and the tube runs of a sufficient number of files at predetermined baffling locations so positioned in the direction of gas flow to form minor ranks of tube runs positioned intermediate said major ranks to occupy said lanes existing between said major ranks and thereby preclude the presence ofdamaging standing wave vibrations caused by the gas stream flowing past the tube bundle.

2. The apparatus of claim 1 wherein the center line spacing between tube runs in a file is substantially twice the diameter of said tube runs and at least one file of tube runs at each of said predetermined baffling locations is positioned substantially midway between said major ranks of tube runs in the direction of gas flow to form said minor ranks.

3. The apparatus of claim 1 wherein the center line spacing between tube runs in a file is substantially greater than twice the diameter of said tube runs and at least two adjacent files of tube runs at each of said predetermined baffling locations are positioned to form a plurality of minor ranks of tube runs between each major rank of tube runs, there being a sufficient number of minor ranks intermediate successive major ranks to preclude the presence of damaging standing waves caused by the gas stream flowing past the tube bundle.

4. The apparatus of claim 1 wherein laterally adjacent pairs of tube run files are supported by support means common to both files and at least a pair of commonly supported files of tube runs at each of said predetermined baffling locations is so positioned in the direction of gas flow to form said minor ranks of tube runs.

5. The apparatus of claim 4 wherein the center line spacing between tube runs in a file is substantially twice the diameter of said tube runs and at least one pair of commonly supported adjacent files of tube runs at each of said predetermined baffling locations is positioned substantially midway between said major ranks of tube runs in the direction of gas flow to form said minor ranks.

6. The apparatus of claim 4 wherein the center line spacing between the tube runs in a file is substantially greater than twice the diameter of said tube runs and at least two pairs of commonly supported adjacent files of tube runs at each of said predetermined bafiling locations are positioned to form a plurality of minor ranks of tube runs between each major rank of tube runs, there being a sufficient number of minor ranks intermediate successive major ranks to preclude the presence of damaging standing waves caused by the gas stream flowing past the tube bundle. 

1. In combination a tube bundle within a duct through which a gaseous stream is conveyed and wherein the tube runs of the tube elements of said bundle are disposed transversely of the direction of flow of said stream, with there being numerous tube runs arranged in a plurality of aligned files, the tube runs in each file being parallelly spaced in the direction of gas flow, the tube runs of a substantial majority of said files so positioned and spaced in the direction of gas flow to form parallelly spaced major ranks of tube runs, each rank extending laterally across the gas stream and comprised of tube runs in spaced side by side relation, adjacent major ranks creating lanes therebetween extending laterally of the gas stream, and the tube runs of a sufficient number of files at predetermined baffling locations so positioned in the direction of gas flow to form minor ranks of tube runs positioned intermediate said major ranks to occupy said lanes existing between said major ranks and thereby preclude the presence of damaging standing wave vibrations caused by the gas streaM flowing past the tube bundle.
 2. The apparatus of claim 1 wherein the center line spacing between tube runs in a file is substantially twice the diameter of said tube runs and at least one file of tube runs at each of said predetermined baffling locations is positioned substantially midway between said major ranks of tube runs in the direction of gas flow to form said minor ranks.
 3. The apparatus of claim 1 wherein the center line spacing between tube runs in a file is substantially greater than twice the diameter of said tube runs and at least two adjacent files of tube runs at each of said predetermined baffling locations are positioned to form a plurality of minor ranks of tube runs between each major rank of tube runs, there being a sufficient number of minor ranks intermediate successive major ranks to preclude the presence of damaging standing waves caused by the gas stream flowing past the tube bundle
 4. The apparatus of claim 1 wherein laterally adjacent pairs of tube run files are supported by support means common to both files and at least a pair of commonly supported files of tube runs at each of said predetermined baffling locations is so positioned in the direction of gas flow to form said minor ranks of tube runs.
 5. The apparatus of claim 4 wherein the center line spacing between tube runs in a file is substantially twice the diameter of said tube runs and at least one pair of commonly supported adjacent files of tube runs at each of said predetermined baffling locations is positioned substantially midway between said major ranks of tube runs in the direction of gas flow to form said minor ranks.
 6. The apparatus of claim 4 wherein the center line spacing between the tube runs in a file is substantially greater than twice the diameter of said tube runs and at least two pairs of commonly supported adjacent files of tube runs at each of said predetermined baffling locations are positioned to form a plurality of minor ranks of tube runs between each major rank of tube runs, there being a sufficient number of minor ranks intermediate successive major ranks to preclude the presence of damaging standing waves caused by the gas stream flowing past the tube bundle. 